Hot Cocoa Sauce for Icecream

Boil together one and one-½ cupfuls of water and one cupful of sugar for two minutes; add one tablespoonful of arrowroot dissolved in a little cold water, stir for a moment, then boil until clear. Add two tablespoonfuls of cocoa which has been dissolved in a little hot water and a tiny pinch of salt and boil three minutes longer. Take from the fire and add one teaspoonful of vanilla.